This invention relates to amplifiers and processes for amplifying electric signals, and more particularly, to electrical devices relying upon magnetoresistance effects to provide power amplication.
State-of-the-art magnetoresistance amplifiers such as those disclosed in U.S. Pat. No. 3,382,448, granted to Paul E. Oberg, et alii, are constructed with a signal circuit overlying a thin-film of a magnetic material. There, a slab of a magnetic material forms an element of a sense circuit magnetically coupled to an equal area of the signal circuit. The magnetization vector of the sense circuit has a preferred axis alignment. The circuits are oriented so that current in the signal circuit creates a magnetic signal field that rotates the magnetization vector about its preferred axis orientation. Note that in a uniaxially anisotropic film the preferred axis is the easy axis, while in an isotropic film the preferred axis is the bias field axis. Other amplifiers are constructed with the signal circuit sandwiched between opposite thin-films of magnetic material having antiparallel magnetization. As can be shown by performing a minimization of free-energy calculation (e.g., see D. O. Smith, Journal of Applied Physics, volume 29, at 274; 1958), if the signal field is applied along the hard axis of the magnetoresistive element and the zero signal orientation of the magnetization vector, M, is along the easy axis, the rotation of the magnetization vector away from its zero signal orientation by the magnetic field created by a signal current is: EQU (H.sub.s /H.sub.k)=SIN .phi., (1)
which becomes: EQU (H.sub.s /H.sub.k).perspectiveto..phi. (2)
for small signals. In practice, the power gain provided by articles of the type described here ranges from less than one to about ten.
A thin-film is a layer of material having a thickness between one hundred angstroms and one hundred thousand angstroms. "Ferro-magnetic" describes a material with a relative permeability that is greater than one in value and that depends upon the magnitude of the magnetizing force.